Feature/sections identifier

Contains the following:
1. Check for resource_link_id match with current session
2. URL changes for the above
3. Check section's course id for match with current session
4. Error handling for 1 and 3 above
 Note: unit tests (new and fixes for ones broken by above changes) to follow in another pull request
This could be shortened to `return resource_link_id == request_resource_link_id`.  You may want to consider whether this even makes sense to be a utility method given how simple the check is that's being done.